Photoelectric conversion elements are used in various photosensors, copying machines, solar cells, and the like. These photoelectric conversion elements have adopted various systems to be put into use, such as elements utilizing metals, elements utilizing semiconductors, elements utilizing organic pigments or dyes, or combinations of these elements. In particular, solar cells using non-exhaustive solar energy do not necessitate fuels, and besides can utilize an inexhaustible clean energy; full-fledged implementation thereof is being highly expected. Among these, research and development of silicon-based solar cells have long been in progress. Many countries support the silicon-based solar cells in policy-wise considerations, and thus they are progressively prevailed. However, silicon is an inorganic material, and hence it has its own limitations in terms of improving throughput, cost, and the like.
Under such circumstances, research is being vigorously carried out on dye-sensitized solar cells. Especially, the research results by Graetzel et al. of École Polytechnique Fédérale de Lausanne in Switzerland is recognized as a turning point. They employed a structure in which a dye formed from a ruthenium complex was fixed at the surface of a porous titanium oxide thin film, and realized a conversion efficiency that was comparable to that of amorphous silicon. Thus, the dye-sensitized solar cells that can be produced even without using an expensive vacuum apparatus instantly attracted the attention of researchers all over the world.
Hitherto, as metal complex dyes to be used in photoelectric conversion elements, dyes generally called as N3, N719, Z907, and J2 have been developed.
Recently, a Ru metal complex dye is proposed, having a particular substituent-having [4-styryl-2-(3-trifluoromethyl)-1H-pyrazole-5-yl] pyridine of a bidentate ligand and 4,4′,4″-tricarboxy-terpyridine of a terdentate ligand (see Patent Literature 1). A novel metal complex is also proposed, having a particular 2,6-bis(nitrogen-containing aromatic ring) pyridine of a terdentate ligand and 4,4′,4″-tricarboxy-terpyridine of a terdentate ligand (see Patent Literature 2).
Further, N719, Black Dye is proposed, having a carboxyl group neutralized with an alkali compound in order to prevent dye association, the carboxyl group playing as a roll of adsorbing it on the surface of semiconductor fine particles (see Patent Literature 3).